1. Field of the Invention
This invention is related to the dimensional inspection of internal spaces. More particularly, it relates to an apparatus that assists with the measurement of spaces using standard small probes to provide a measurement of the space to a high degree of accuracy. The apparatus is capable of being positioned and locked into the space to be measured and later removed. This invention is also a method of measuring a space using the apparatus.
2. Description of Prior Art
Large internal space dimensional inspection has previously involved the use of unique probes designed for such large spaces. These large space probes were similar to more standard small probes but they lacked the ability to maintain good surface contact with the boundaries of the space to be measured which resulted in errors in measurements and an inability to reproduce consistent measurements of the same space.
An internal shim has at least one dimension that is less than the dimension of a space defined by boundaries that is to be accurately measured. The internal shim has a chassis that defines a plurality of push rod passages and a plurality of pairs of gripper openings. Each gripper opening of a pair of gripper openings are on opposite sides of the chassis and are separated by the push rod passage. The internal shim has a shim top end that is wider than the boundaries of the space to be measured. The shim top end has a top and a bottom and defines a plurality of push rod openings therethrough. The shim top end is attached to one end of the chassis such that the push rod passages and the push rod openings are aligned. A push rod is disposed within each of the push rod passages and passes through a push rod opening. Each push rod has a length which is approximately equal to the length of the push rod passage. The push rod has a cross sectional dimension that is uniform along its length. However, it also has a plurality of sections, which correspond to the pairs of gripper openings, wherein the cross sectional dimension is larger than the normal uniform dimension and tapers from that dimension along a portion of its length to a smaller uniform dimension. A gripper element is disposed within each gripper opening. The gripper element comprises a gripper and a rod attached thereto. The top end of the gripper rod is rotatably attached to the chassis. Placement of the gripper elements is such that the gripper portion of the gripper element is immediately adjacent to those sections of the push rod having a tapered rather than uniform cross sectional dimension. The gripper openings are of sufficient size such that the grippers can extend from the chassis body.
An arm, one end of which is pivotably attached to the top of the shim top end, passes over each push rod opening. The arm is adapted to co-act with the top end of the push rod. The other end of the arm is adjustably attached to the top of the shim top end. A spring mechanism is disposed between those sections of the push rod having a tapered cross sectional area and the chassis within the push rod passage. The spring mechanisms are disposed between each of those tapering sections except for the section closest to the bottom end of the push rod.
During use, the grippers are forced from the chassis against the boundaries of the space to be accurately measured. The grippers hold the internal shim firmly in the space to be measured. The grippers are forced from the chassis by the action of the sections of the push rod having a tapered cross sectional area acting against the grippers when the arm is adjusted, such that the push rod moves downward relative to the push rod passage. When the measurement of the space is complete, the arm is adjusted such that the sections of the push rod having a smaller uniform cross sectional dimension are between the grippers, allowing the grippers to return within the chassis and permitting the internal shim to be removed from the space.
In a second preferred embodiment, the chassis also defines a plurality of pairs of guide channels through which a standard small probe can pass. In one pair of guide channels, each guide channel is on opposite sides of the chassis. Each guide channel is continuous along the entire length of the chassis. This guide channel is aligned with a guide opening in the shim top end that is also large enough for a standard measurement probe to pass. In this way, measurements of the space to be measured can be periodically repeated along a location that is fixed relative to the dimensions of the internal shim.
A method of accurately measuring a space defined by boundaries using the internal shim and a standard small probe comprises the following steps:
1) measuring and recording the thickness dimension of the shim between the opposing guide channels at the location where measurements will occur;
2) placing the internal shim within the space to be measured;
3) adjusting the arms such that the internal shim is firmly fixed in the space to be measured;
4) inserting a standard small probe in the first guide channel of the internal shim and one boundary of the space to be measured;
5) measuring and recording a plurality of distances from the bottom of the guide channel of the internal shim to the boundaries of the space to be measured using the standard small probe;
6) repeating steps 4 and 5 to measure spaces on the oposite side of the chassis.
7) adjusting the arms such that the internal shim is no longer fixed in the space to be measured;
8) removing the internal shim from the space; and
9) summing the recorded measurements to determine the dimensions between the boundaries of the spaces to be measured.
Further details and advantages of the invention may be seen from the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals represent like parts.